Experimental Production of Endolymphatic Hydrops

Low-grade adenocarcinoma of endolymphatic sac origin

We present a case of papillary cystic low-grade adenocarcinoma of endolymphatic sac origin. These tumors are very rare and only a few cases have been reported in literature. They have a protracted clinical course causing progressive invasion and bony destruction. Radiologically, they appear as a heterogenous lobulated vascular mass, invading bone and compressing surrounding structures. Histologically, these tumors are composed of uniform population of cells, resembling normal endolymphatic sac epithelium. This causes considerable diagnostic difficulty. A strong index of suspicion along with clinical and radiological correlation is essential to arrive at a correct diagnosis. In some bilateral cases, association with von Hippel-Lindau disease has been noted. Radical mastoidectomy and temporal bone resection, which may sometimes necessitate sacrifice of cranial nerves, is the treatment of choice.

Microscale analysis of proteins in inner ear tissues and fluids with emphasis on endolymphatic sac, otoconia, and organ of Corti

Here we describe preparatory techniques adapted for the study of proteins of inner ear tissues and fluids that have allowed us to apply state-of-the-art analytical techniques in spite of the minute size and anatomical complexities of this organ. Illustrative examples address unresolved issues of functional and clinical significance. First, we demonstrate how quick-freezing and freeze drying prevents artifacts that arise from sampling endolymphatic sac (ES) content in the liquid state. This set the stage for the generation of the first protein profile of the ES. Identification of crucial proteins will help elucidate mechanisms of endolymph volume regulation and pathogenesis of Meniere's disease. Second, we show how a unique situation allowed identification of otoconial proteins by mass spectrometric analysis without prior separation and we discuss possible roles for these minor otoconins in otoconial development and prevention of degenerative diseases that affect balance. Finally, we demonstrate techniques for the precise dissection of organ of Corti and its substructures, while preserving their near normal chemical state. We extended an earlier study in which we identified a novel calcium-binding protein by IEF, oncomodulin, localized in the outer hair cells and show here the applicability of prefractionation for the screening of calcium-binding proteins of organ of Corti. These studies demonstrate how advanced preparatory and analytical techniques can be applied to studies of the inner ear.

Relationship of vestibular aqueduct and inner ear pressure in Ménière's disease and the normal population

OBJECTIVE

Etiopathogenesis of Ménière's disease has not been resolved. The principal histopathologic finding in this disease is endolymphatic hydrops. The majority of radiologic and histopathologic studies demonstrated a narrow vestibular aqueduct in Ménière's disease. There is no study in the literature investigating the relationship between inner ear pressure and vestibular aqueduct dimensions. Static acoustic compliance is a noninvasive procedure that is thought to measure perilymphatic pressure at the footplate. An increase in mechanical fluid pressure in the inner ear is transmitted to the footplate of the stapes. This causes a reduction in the compliance at the drum. The aim of this study is to investigate the relationship between vestibular aqueduct dimensions and static acoustic compliance in Ménière's disease and the normal population.

STUDY DESIGN

Prospective study.

METHODS

Forty patients with Ménière's disease and 40 healthy individuals with no otolaryngologic disorders were the subjects of this study. Each group was further divided into two according to static compliance value (normal and low static compliance). In these four groups dimensions of vestibular aqueduct were determined radiologically by high-resolution computerized tomography and correlated with normal and low static acoustic compliance values (normal and high perilymphatic pressure).

RESULTS

The results demonstrated that vestibular aqueduct is narrower in patients with Ménière's disease than the normal population. However, there is no relationship between vestibular aqueduct dimensions and inner ear pressure obtained by static acoustic compliance measurements.

Endolymphatic sac tumor: a case report

Papillary tumors of the temporal bone are aggressive neoplasms which may occur sporadically or as a part of von Hippel-Lindau disease. The term 'endolymphatic sac tumor' identifies the origin of these rare tumors. The clinical manifestations are sensorineural hearing loss, facial paralysis, cerebellar disorders and vertigo. The tumor is locally invasive, destructive and hypervascular exhibiting consistent imaging and histopathologic features. The treatment of choice is the total removal of the lesion although complete excision of the advanced lesion is nearly impossible due to the anatomic complexity of the endolymphatic sac and distinct patterns of extension. We present a 50-year-old male patient with endolymphatic sac tumor with left sided sensorineural hearing loss and review the literature.

Endolymphatic sac tumors: report of three cases

OBJECTIVE AND IMPORTANCE

We present three cases of endolymphatic sac tumors and review the previously published cases. Despite frequent extension to the cerebellopontine angle, these rare tumors have only recently been recognized by neurosurgeons.

CLINICAL PRESENTATION

A 26-year-old man developed a progressive hearing loss, revealing an intrapetrous retrolabyrinthine tumor on the right side. A 28-year-old woman experienced a left cerebellopontine angle syndrome, with a lytic intrapetrous mass extending into the cerebellopontine angle. A 38-year-old woman presented with an intracranial hypertension syndrome caused by a tumor of the jugular foramen.

INTERVENTION

For the first and second patients, the tumors originated from the operculum of the endolymphatic sac. Total removal was achieved, via a transpetrosal approach, in these two cases. No recurrence was detected after a 20-month follow-up period. For the third patient, the tumor originated from the distal part of the sac. Recurrence was observed 8 years after subtotal removal via a retrosigmoid route. Histological analysis revealed a papillary-cystic adenocarcinomatous pattern in all cases, without features of aggressiveness.

CONCLUSION

Endolymphatic sac tumors are locally invasive neoplasms characterized by bipolar intrapetrous and posterior fossa involvement. The anatomic complexity of the endolymphatic sac may explain the distinct patterns of extension of these tumors. Early radical surgery is related to good outcomes.

Endolymphatic sac tumors: histopathologic confirmation, clinical characterization, and implication in von Hippel-Lindau disease

The term "endolymphatic sac tumor" (ELST) was coined to identify the likely origin of aggressive papillary tumors of the temporal bone. To evaluate the validity of this designation, the temporal bone collection at the Massachusetts Eye and Ear Infirmary was accessed in an effort to determine the pathologic relationship between these tumors and the endolymphatic sac. The search resulted in the identification of a de-novo papillary epithelial lesion arising within the confines of the endolymphatic sac in a patient with von Hippel-Lindau (VHL) disease who harbored a large, destructive ELST in the opposite temporal bone. This finding provides the most substantial evidence to date regarding the origin of the ELST and the accuracy of its nomenclature. Seven additional clinical cases of ELST were identified and analyzed in order to define the natural history of these tumors. All patients had a history of sensorineural hearing loss diagnosed an average of 10.6 years prior to tumor discovery. The presence of a polypoid external auditory canal mass, facial paralysis, and evidence of a destructive mass arising on the posterior fossa surface of the temporal bone were common physical and radiographic findings. The management of these patients, as well as those who are probably prone to such tumors (i.e., VHL patients), is discussed.

Functional changes associated with experimentally induced endolymphatic hydrops

A guinea pig model with surgically induced endolymphatic hydrops of the inner ear has been developed and studied over the past thirty years. The aim of such studies is to obtain insight into physiological processes associated with endolymphatic hydrops in man and in particular in Menière's disease where endolymphatic hydrops is systematically encountered at post-mortem examination of the temporal bones. The present review attempts to draw together the data pertaining to functional modifications of inner ear function in the animal model. For simplicity the data are categorised under five main titles: electrochemical modifications, electrophysiological modifications, pressure and hydrops, sensitivity to other insults and vestibular dysfunction. One of the most striking observations that can be made is that the data originating from different authors are very variable. There is, however, some evidence suggesting that the evolution of the auditory dysfunction could be considered as consisting of a series of different phases. This kind of information could serve as a basic framework for future research on the animal model.

Cochlear and cerebrospinal fluid pressure: their inter-relationship and control mechanisms

The patency of the cochlear aqueduct is a key factor in intra-cochlear hydromechanics. If patent, the cerebrospinal fluid (CSF) provides the reference pressure for the perilymph and also to a large extent the endolymph, since Reissner's membrane can only withstand a relatively small pressure differential. The aqueduct often becomes sealed as a natural process of ageing. In this instance the reference pressure is from a source, its position unknown, within the boundaries of the cochlea itself. Relatively large and rapid changes in the cerebrospinal fluid pressure may result from everyday events such as coughing (ca. 175 mm saline) and sneezing (ca. 250 mm saline). The resistive nature of the cochlear aqueduct and the mechanical compliance of the cochlear windows are probably important factors in limiting the amount of stress, and therefore possible damage, which may occur to the cochlea and cochlear windows for a given pressure change within the CSF system. A narrow aqueduct and compliant cochlear windows reduce the risk of structural damage. In practice, this should mean that the risk of structural damage will be increased by any process which reduces the compliance of one or both of the cochlear windows, for example, extremes of middle ear pressure perhaps brought about by Eustachian tube dysfunction or rapid barometric pressure changes. Techniques are now available which provide non-invasive indirect measures of perilymphatic pressure and CSF-perilymphatic pressure transfer. The tympanic membrane displacement measurement technique has been used to provide reliable measures of perilymphatic pressure and CSF-perilymphatic pressure transfer on an individual subject basis.(ABSTRACT TRUNCATED AT 250 WORDS)

Elevation of inner ear antibody levels following direct antigen challenge of the endolymphatic sac

The effect of direct antigen challenge of the endolymphatic sac (e.sac) on inner ear antibody levels was investigated in guinea pigs. Two weeks following e.sac antigen inoculation, perilymph antibody levels to keyhole limpet hemocyanin (KLH) were found to be significantly elevated in the challenged ear of those animals compared to the unchallenged, opposite ear. Moreover, when the endolymphatic duct (e.duct) in a group of animals were obstructed prior to antigen challenge of their e.sac then the rise in perilymph antibody was prevented. The local accumulation of plasma cells and lymphocytes in the perisaccular space and e.sac lumen was seen following these antigen injections. These experiments suggest that inner ear antibody emanates from the e.sac and reaches the perilymphatic compartment along the route of the e.duct. Furthermore, these findings emphasize the central role of the e.sac in inner ear immunity.

Cochlear and vestibular functions of the rat after obliteration of the endolymphatic sac

A combined morphological and physiological study on the effect of saccus obliteration on the cochlea and the vestibular labyrinth of the rat is presented. Endolymphatic hydrops was successfully induced in 49% of the animals. It was frequently associated with fistulae of the membranous wall and degenerative changes in the organ of Corti and spiral ganglion. In hydropic ears electrocochleography revealed a CAP threshold increase only in those cases where hydrops was associated with loss of hair cells and ganglion cells. In two of these animals also an increased negative SP was present. Static otolith reflexes were found to be normal in all hydropic ears despite severe lesions of the saccule in some of these. Abnormal canal reflexes measured by electronystagmography and cupulometry were established in animals with hydrops of the semicircular canals and in one animal with a fistula of the saccule.

Early hair cell loss in experimental hydrops

One, 2, and 4 months after surgical obliteration of the endolymphatic sac, the sequence of degenerative changes in the organ of Corti of the guinea pig was studied. The block surface technique with interference differential (Nomarski) microscopy was used for this investigation to study the morphological changes in the organ of Corti. The hair cell loss was calculated and mapped in cytocochleograms. One month postoperatively a minimal loss of only outer hair cells was observed in the apical cochlear turn. At 2 months a progression of outer hair cell loss was seen, which proceeded in the 4-month group. At 4 months the inner hair cells showed a slight tendency to degenerate, again beginning in the most apical part of the cochlea.

Hydrostatic pressure measurements of endolymph and perilymph in a guinea pig model of endolymphatic hydrops

The primary histologic correlate of Menière's disease is endolymphatic hydrops. From this, many investigators have postulated the existence of endolymphatic hypertension, although there have been no measurements published to substantiate this concept. Seventy guinea pigs, surgically treated with right endolymphatic duct obstruction, were later assessed by use of a micro-electrode technique that measured their endolabyrinthine hydrostatic pressures. For 21 of these animals, the pressures of both scala tympani (Pst) and scala media (Psm) of both ears of each animal were successfully measured. Similar measurements were made in a control group of 25 guinea pigs that had not undergone any previous surgery. For normal ears--as well as those with hydrops-pressure differences between perilymph and endolymph (Psm - Pst) varied around 0 +/- 2.0 mm Hg. When only the right (obstructed) ears were considered, there appeared to be a slight, relative pressure elevation (p less than 0.05) in scala media during the first 7 days after endolymphatic duct obstruction-and in those ears with EP, less than 70 mV. The magnitude of this pressure difference that can be attributed to the state of endolymphatic hydrops-and not to natural variability-is calculated (within 95% confidence limits) to be less than 0.5 mm Hg.

Longitudinal flow of macromolecules in the endolymphatic space of the rat. An autoradiographical study

Secretion and resorption of sulphated glycoproteins by the epithelial lining of the endolymphatic space of the rat were studied autoradiographically with the use of 35SO4 as a selective marker. This isotope was found to be incorporated into the sensory area of cristae and maculae and a small area of epithelial cells adjacent to the sensory epithelium. Thereafter 35S-labelled glycoproteins were secreted into cupulae and otolithic membranes. No such process could be established in the tectorial membrane. From the gradual disappearance of 35S-labelled glycoproteins from cupulae and otolithic membrane coupled with an accumulation of this substance in the lumen of the endolymphatic sac, the existence of a longitudinal flow under physiological conditions could be concluded. Resorption of glycoproteins by the saccus epithelium was found to be very slow. Accumulation of 35S-labelled glycoproteins in the endolymphatic duct after saccus obstruction indicates that, in addition to the endolymphatic sac, also the duct contributes to the mechanism underlying the longitudinal flow of macromolecules.

An experimental study of inner ear pathology due to NaCl on the round window

An animal experiment was performed to evaluate structural and ultrastructural changes to the inner ear as a result of placing 3-4 crystals of reagent grade sodium chloride (NaCl) on the round window membrane. Chinchillas were sacrificed at 8 and 24 hours after treatment and the cochlear and vestibular tissues were examined by light microscopy and scanning electron microscopy. Inner ear pathology consisted of destruction of both sensory and supporting cells in the basal turn of the organ of Corti, atrophy of the stria vascularis and alterations to the otoconia and the maculae and ampullae of the vestibular system. This study demonstrates that NaCl in the middle ear does not provide a model for Meniere's disease as previously suggested by Arslan. It may, however, be utilized in the destructive treatment of selected inner ear disorders.

Fistulae in the membranous labyrinth

Fistulization at various parts of the membranous labyrinth has been currently in use as one of the treatments for the symptoms of Meniere's disease. The present report concerns our experience with membranous fistulae in experimental animal ears with and without manifestation of endolymphatic hydrops. The materials presented are mostly new; however, our previous data are also incorporated in order to bring this issue into better perspective. The first part describes the nonproduction aspect of endolymphatic hydrops in the rat, chinchilla, and squirrel monkey after obliteration of the endolymphatic duct in relation to the occurrence of spontaneous fistulae. The second part describes surgical fistulization of the vestibular membranous labyrinth and cochlear duct in order to prevent or control development of endolymphatic hydrops in the guinea pig, the species in which hydrops can be produced consistently. These results are tabulated and analyzed in terms of the pathological consequences that can be expected in performing fistulization of the membranous labyrinths in animals as well as in humans.

Endolymphatic hydrops in the rabbit: auditory brainstem responses and cochlear morphology

A rabbit model of endolymphatic hydrops was studied using detailed functional and cytohistologic methods. Immediately following surgical destruction of the endolymphatic sac and the distal portion of the duct, measures of the evoked auditory brainstem response (ABR) revealed mild to profound losses specific to low- and high-frequency test stimuli while responses to mid-frequency signals remained unchanged for the majority of animals. Rabbits exhibited varying degrees of vestibular upset involving both overt behavior and reduced responses to caloric stimulation. Histologic processing of the plastic embedded cochleae demonstrated distended Reissner's membranes along with extensive damage to apical and basal turn sensory cells and myelinated afferent nerve fibers while the middle portion of the cochlear duct remained relatively unaltered. An atypical pattern of hair cell lesions involving a greater loss for inner than for outer hair cells was identified at the interface between damaged apical sensorineural elements and the normal appearing organ of Corti of the middle turns.

Intracellular and extracellular ion content of the endolymphatic sac

The Cl- activity in the endolymph of the endolymphatic sac and in the cochlear duct was measured with Cl- sensitive double-barreled microelectrodes. The Cl- activity in the endolymphatic sac fluid was lower than in the cochlear duct. A small, positive, DC potential was recorded in the endolymphatic sac. During anoxia, the DC potential decreased while the Cl- activity in the endolymphatic sac increased. The K/Na ratio in the epithelial cells and subepithelial tissue of endolymphatic sac was measured using the LAMMA technique. The K/Na ratio in the epithelial cells decreased after ethacrynic acid injection (60 mg/kg i.v.). These findings suggest that chloride in the endolymphatic sac is actively transported inward and outward.

Inner ear fluids dynamics and endolymphatic hydrops

The inner ear possesses remarkably stable homeostatic mechanisms for the maintenance of the functional integrity of the inner ear end-organs. The inner ear fluid maintains its homeostasis by a variety of subtle regulatory mechanisms, both locally and systemically. Any disturbance in one of these mechanisms can induce the disruption of homeostasis expressed by ionic, osmotic, or metabolic imbalance between the compartments. This can be manifested as membrane displacement or abnormal functions of the inner ear, depending on the degree of the disturbance. Further studies are necessary to clarify these regulatory mechanisms of homeostasis and those conditions which alter homeostasis which can result in the abnormal functions. Further research along this line is essential in order to understand the etiology of endolymphatic hydrops and also to establish guidelines for possible normalization of this pathological status.

Animal models of endolymphatic hydrops

Endolymphatic hydrops in the animal can be produced by various methods. The most promising is obliteration of the endolymphatic duct in the guinea pig. The extent of hydrops is similar to that of Ménière's disease specimens, but the animals are asymptomatic. A better model, utilizing a less invasive method and having the ability to elicit episodic vestibular symptoms, is needed. There is a reasonable doubt that one of the causes for Ménière's disease lies in the abnormal endolymphatic duct and sac. A wide ablation of such pathologic tissue may provide additional pathogenetic information.

Effect of transverse temporal bone fracture on the fluid compartment of the inner ear

Five temporal bones exhibiting transverse fractures were studied with a view to determining whether such fractures could lead to symptomatic endolymphatic hydrops. Four out of the five temporal bones showed the fracture line traversing the vestibular aqueduct. Two of these four showed complete obstruction of the endolymphatic duct. One of these had an intact membranous labyrinth and severe endolymphatic hydrops. The other had ruptures of the membranous labyrinth and no hydrops. Three ears exhibited partial preservation of auditory and vestibular hair cells and neurons. These findings are consistent with the concept that a transverse fracture may produce endolymphatic hydrops by obstructing the vestibular aqueduct while preserving enough audiovestibular epithelium and neurons to present as symptomatic Menière's disease.

Surgical anatomy of the temporal bone in the chinchilla

The chinchilla is of value in otological research for many reasons, including the surgical accessibility of the majority of structures within its temporal bone. This paper describes the anatomy of the chinchilla's temporal bone, and four surgical approaches to the labyrinth and ossicular chain, three through the bulla and the other via the external canal. No one approach reveals all the temporal bone structures, and each route is therefore more suited to some surgical procedures than others. The cochlea is particularly accessible for microsurgical procedures because it projects into the labyrinthine part of the bulla and because its bony capsule is thin. Surgery in the posterior cranial fossae is both hazardous and difficult; the hazard is bleeding from the venous sinuses which run within the occipital and temporal bones, and the difficulty is the limited access due to the intervening cerebellum and the closeness of the brain stem.

Electron microscopic cochlear observations in bilateral Ménière's disease

Electron microscopic study of the cochleas of an individual with bilateral Ménière's disease revealed the presence of many abnormal sensory cells in the apical regions of the cochleas. The pathological alterations were greater in the left ear with the greater hearing loss. There were some giant cilia, fusion of cilia, and loss of cilia. The outer hair cells contained diffuse cuticular bodies near or basal to the nuclei. Many outer hair cells were retracted away from the reticular membrane. The population of the nerve endings appeared normal. The inner hair cells of the apical turns appeared essentially normal. The spiral ganglia were normal in number and morphology at the apical turns, and a majority of their cell bodies were of the unmyelinated or partly myelinated types. The stria vascularis showed atrophy; however, the magnitude of this change was consistent with that known to occur in the aging ear. In the distended areas Reissner's membrane showed areas devoid of mesothelial cells, as well as atrophic epithelial cells. The blood vessels were no different from other human cochlear vessels. These abnormalities seen in the stereocilia, the outer hair cells, and Reissner's membrane are a matter of fact. We must admit, however, that not enough electron microscopic studies have been performed on ears from aging individuals or ears with other pathologies to state that these changes are unique to Ménière's disease. Furthermore, there is currently insufficient knowledge to predict whether these changes affect auditory function.

Experimental pathogenesis of hydrops

1. The best method for inducing hydrops in guinea pigs is obliteration of the endolymphatic duct. 2. The location of hydrops produced in the guinea pig is comparable to that of Menière's disease. 3. The major histopathological finding in the guinea pig is atrophy of sensorineural elements in the apical turns of the cochlea. 4. The vestibular sensory cell population is rarely decreased, though ultrastructural changes are noted. 5. Attempts to prevent or minimize development of hydrops by surgical fistulization of the vestibular endolymphatic walls or by administration of a diuretic drug, ethacrynic acid, failed in the guinea pig. Treatment of Menière's disease by these means is questionable. 6. Electron microscopy of the organ of Corti in cochleas taken from a patient with bilateral Menière's disease revealed that only a small percentage of te sensorineural elements was abnormal at the apical turns. Thus, it is questionable whether these small ultrastructural changes in the organ of Corti are a major cause of severe hearing loss. 7. In Menière's disease biochemical changes in cochlear fluid and/or changes in motion mechanics of the cochlear duct are probably important factors producing the hearing loss. 8. The present ultrastructural study did not resolve the question of the etiology of Menière's disease.

Effect of fistulae on endolymphatic hydrops

An experiment was performed on 31 guinea pigs to study the effect of fistulae of the horizontal canal, superior canal, common crus, and utricle on the course of experimentally induced endolymphatic hydrops. The effect of fistulae on corresponding parts of normal ears was also studied in an additional 17 animals. The results indicated a remarkable consistency of healing of the fistulae in both groups of animals. Fistulae had no significant effect on the course of endolymphatic hydrops, irrespective of whether the fistulae were made immediately before or several months after obliteration of the endolymphatic duct or whether a polyethylene strut was introduced into the membranous labyrinth. Once again, the functional significance of the endolymphatic sac was clearly apparent, for ablation of the sac consistently produced severe hydrops and atrophic changes in sensory and neural structures. Assuming that the mechanisms of labyrinth repair in the guinea pig are comparable to the higher mammalian ear, it is apparent that procedures designed to surgically fistulize the membranous labyrinth are of questionable value and are probably not rational therapeutic approaches to the management of Ménière's disease.